1. Field of the Invention
This invention relates to program control positioning systems and more particularly to methods and apparatus for generating control programs for such positioning systems by manually imposing forces on the positionable member, generating force feedback signals to control the positioning system to move the member to decrease the forces, and recording successive signals generated within the positioning system.
2. Prior Art
Program controlled positioning systems are widely employed with machine tools, transfer machines, work manipulators and the like. These systems may be broadly divided into point-to-point controls, which move a positionable part to a series of discrete positions commanded on a program without exercising any control over the path or rate of part motion between these points, and continuous path systems which exercise control over both the position and rate of motion of the positionable member through an entire programmed path. Control programs for these positioning systems typically consist of a series of numerical commands which define either the series of points that the part is to assume or the nature of short segments of the desired motion along a continuous path.
Preparation of these programs requires knowledge of the positional capability of the machine and a description of the process to be performed. If the machine has a very limited positional capability programs may be quite simply generated; i.e., a cut-off machine may have a stop positionable along a single axis. A program for forming a series of parts of different lengths simply involves the single axis coordinates of the series of positions the stop must assume. As the number of controlled axes increases the programming task becomes more complicated. Some part manipulators may have a large number of degrees of freedom so that they are capable of moving parts in the same versatile way as the human hand. In these systems a particular motion may often be accomplished by a practically infinite number of combinations of motions along the various controlled axes and the programming task is extremely complicated.
In order to avoid the complexities of preparing a control program based on information relating to the machine capability and the operations to be performed, it has been proposed to manually move the positional member through a desired path and to record the resulting outputs of position transducers associated with each of the machine's controlled axes. These transducers need not be specially provided for the purpose of generating control programs since they form part of the closed loop drive systems typically employed with these program controlled machines. U.S. Pat. No. 2,475,245 discloses a control system for a lathe driven by an analog program recorded on magnetic tape. To prepare a program the lathe operator drives the machine using the manual controls to form a sample part and the output signals from synchros in the positioning system and recorded. The recorded program may then be played back to automatically control the lathe to form duplicates of the part. U.S. Pat. No. 3,890,552 discloses a program controlled manipulator having manually controllable means for generating control signals which may either be recorded for later play-back or may be used to directly move the manipulator while the outputs of the machine's position transducers are recorded. If the manipulator has a large number of independent degrees of freedom this axis-by-axis type of manual control proves awkward and difficult.
It is accordingly a broad object of the present invention to provide a method and apparatus for generating control programs for a position control system which overcomes these disadvantages of the prior art.
To achieve this object the present invention draws upon another, independent line of technology which involves the use of load cells to measure forces exerted between workpieces held in the grippers of a manipulator and independent parts that the supported workpieces are to be assembled with. These load cell signals are used to modify programmed position commands to achieve desired relationships between the supported workpiece and the independent part. Using this mode of feedback may simplify the programs for various assembly operations. This technique, termed "force feedback steering" is described in a thesis entitled "Force Feedback Steering of a Teleoperator System" by Roland Groome, Jr., submitted to the Massachusetts Institute of Technology on Aug. 14, 1972.